Cooling cells and receptacles having extremely insulated hollow walls into which a fluid, usually a pumpable liquid, but frequently a slurry, carrying the latent cold can be introduced. The pumpable latent cooling medium can be stored in the hollow wall and can enter into heat exchange through the thermally conductive inner wall with the interior of the receptacle and can maintain the temperature of any optional article or substance which can be stored therein. The uniform cooling effect is maintained as long as the phase transformation of the latent cooling liquid continues. That transformation may be, for example, in the case of a slurry of ice in water or brine, the melting of the ice. When the phase transformation is complete, the used latent cooling fluid can be replaced by a fresh latent cooling fluid and the cooling process continued. The receptacle can be a fixed receptacle or a mobile receptacle and the system for supplying the fresh latent cooling fluid can be provided at a fixed location to which the receptacle can be moved.
During the cooling operation the specifically heavier phase, usually the phase resulting from the phase transformation, tends to settle toward the bottom of the hollow wall of the receptacle, while the lighter phase, usually the phase undergoing transformation tends to rise. The heavier phase having undergone transformation no longer tends to act as a heat sink capable of absorbing heat from the interior of the vessel.
With increasing phase transformation, as a result of this phase separation, the temperature distribution over the height of the vessel tends to become less uniform and as a result there may be nonuniform cooling of the contents of the receptacle. Nonuniform cooling, when it does arise may be in violation of regulations for the storage of certain articles or substances, for example biological materials or foodstuffs. It also may be undesirable and thus can be avoided by appropriate changeover or replacement of the latent cooling medium.
The latent cooling medium normally contains air or gaseous components which can be entrained in the pumped medium and during the cooling process tends to separate out and rise to the top of the hollow wall above the lighter phase therein.
In conventional refilling operations, this air and gas cannot be completely discharged and tends to accumulate additively with excessive replacement operations, thereby reducing the cooling capacity and cooling efficiency.
Efforts have been made in the past to reduce the collection of gas within the vessel wall and hence the reduction of capacity associated therewith by limiting the separation of, for example, the water and ice within the latent cooling fluid, e.g. by baffling the interior of the hollow walls or otherwise impeding the phase separation. The result is a zig-zag arrangement within the interior. This system does result in a uniform cooling effect upon the articles to be cooled but is associated with other drawbacks. For example, the structure is expensive to fabricate and is associated with a higher weight of the hollow wall receptacle. The flow resistance to displacement of the latent cooling fluid is high which can draw out or delay the filling operation. The zig-zag flow passages preclude simple discharge of the latent cooling medium and often require that the receptacle be tipped to effect complete discharge or require blowing out the medium with compressed air. The problem of gas build-up is only partially solved by this approach.